Vocational vehicles like dump trucks, cement mixers, buses, refuse trucks, and fire engines have been almost exclusively diesel-powered for decades. The engines in these applications are often smaller in size than what you’ll find in Class 8 trucks, but at the same time are notably larger than the power plants used in light-duty vehicles. It’s time for a comprehensive “best diesel engine” and “worst diesel engine” list that covers medium-duty diesel engines. From the renowned and nearly-unkillable International DT466 to the dreaded, triple-nickel Cummins V-8, five of the greatest oil-burners ever designed make the cut below—along with a few candidates most would agree belong in the scrap yard.